What is Drama?

I have lately been pondering the definition of role-playing games. But definitions have a way of demanding other definitions. The regress has led me to wonder "what is drama?" Drama is commonly used today to refer to a story that is neither comedy nor tragedy, but its origin incorporated both tragedy and comedy, as theatrical types. That was the ancient Greek definition of drama, who distinguished drama not as a genre, but as a mode, distinct from the modes of lyric poetry and epic. And this distinction in turn was based on differences between mimesis (representation) and diegesis (narration), where epic poems narrated while dramatic theater represented.

According to some sources, however, movies are considered an epic (narrative) form utilizing dramatic elements, rather than a dramatic form utilizing narrative elements. The idea is that the cinematographer and editor are narrating - when the action jumps from one scene to another, for instance, that's a narrator saying "meanwhile, over here..." And so the "world" of the movie is called its diegetic world. A subtitle is non-diegetic, as it doesn't take place inside the world of the movie.

Yet doesn't that sound like mimesis? In other words, is there a genuine difference between showing and telling, if that difference does not lie in the difference between the oral and visual? And if mimesis and diegesis are the same, then epic and drama are the same, and the term becomes meaningless.